Quote - I wonder about that. some P6 clothes are in the props folder but they act like figures. How it that possible, is the extension meaningless?

The extension only determines what files show up in each section.
It has no bearing on the content of the file, Poser is more or less fine with processing anything from any file.

The only special processing is for HR2 files (remove current parented hair prop), HD2 files (ask which hand you want to apply to) and possibly PZ2 files (can't be used for figures IIRC).